1. Field of the Invention
The present invention relates to hydraulic cylinders, and, in particular, to hydraulic cylinders used to temporarily support the roof of a mine pending more permanent roof reinforcement.
2. Description of the Invention Background
As is well known in the underground mining industry, during mining operations a mining machine having a rotary cutting member is advanced into an area to be mined to remove material therefrom. Of course, the weight of the earth above the removed material must be supported to avoid collapse of the mine's roof. Typically, mining machines are provided with ancillary hydraulic cylinders which may temporarily support the mine roof, preferably during the advancement of the miner, until an approved permanent roof support, e.g., bolts, wooden posts, or cribbing, is installed.
Those skilled in the art are highly cognizant of the fact that much of the material to be mined which was formerly resident in relatively taller seams has heretofore been removed. As such, many mines currently being operated, and even more in the future, will face relatively lower coal seams. Due to the excessive costs associated with the mining and removal of unnecessary material, it is highly preferable for mining machines to only remove the minimum amount of material required from the seam. Necessarily, therefore, mining machines are constructed of lesser height to fit within such lower seams. Similarly, the temporary hydraulic roof support cylinders must be of compact height to fit within the lowest of seams. However, in certain areas of the mine, the temporary roof support cylinders must be capable of supporting considerably higher roofs. Accordingly, the competing interests of compact size, sufficient load-bearing capacity and sufficient extensibility have not been heretofore adequately addressed in the industry.
In addition, those skilled in the art recognize that it is important that temporary roof support cylinders be extensible both downwardly to engage the support surface of the mine floor, and upwardly to support the mine roof. However, it has been proven desirable that temporary mine roof support cylinders be independently extensible in the downward and upward directions. Heretofore, the art has been devoid of a temporary mine roof support cylinder which was of compact design yet of sufficient capacity, extensibility and flexibility of operation to meet the challenging needs of the industry.
The subject invention is directed toward an improved temporary mine roof support apparatus which overcomes, among others, the above-discussed concerns in the mining industry and which provides a high capacity, sufficient reach support cylinder in a compact, flexibly operable configuration.